Aero compression combustion drive assembly control system

ABSTRACT

A control system for an aero compression combustion drive assembly, the aero compression combustion drive assembly having an engine member, a transmission member and a propeller member, the control system including a sensor for sensing a pressure parameter in each of a plurality of compression chambers of the engine member, the sensor for providing the sensed pressure parameter to a control system device, the control system device having a plurality of control programs for effecting selected engine control and the control system device acting on the sensed pressure parameter to effect a control strategy in the engine member A control method is further included.

RELATED APPLICATION

This application is a continuation of application Ser. No. 13/646,576filed Oct. 5, 2012, which claims the benefit of U.S. ProvisionalApplication No. 61/543,624 filed Oct. 5, 2011, each of which is herebyfully incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is a compression combustion drive assembly. Moreparticularly, the present invention is a compression combustion driveassembly adapted for use in the aviation environment.

BACKGROUND OF THE INVENTION

At least since WWII, light aircraft (General Aviation and, morerecently, drones) have been powered by an air cooled, gasoline fueledengine that was typically an opposed six cylinder arrangement. Thisengine was fueled by very high octane AvGas. The non availability ofAvGas in the remote portions of the world has meant that generalaviation was unavailable in such area, the very areas of the world thatneed general aviation services the most. More recently it has been seenthat refineries have been reluctant to produce AvGas, thereby stretchingthe world's supply. While all fuels are not cheap, AvGas has beenespecially costly.

In contrast to the relative scarcity and costliness of AvGas, relativelyinexpensive diesel fuel and/or jet fuel (JP) is much more generallyavailable throughout the world. While the quality of such fuel can varygreatly, a compression combustion engine can burn either diesel fuel orjet fuel (JP) about equally as well. The variances can be recognized asvariance in the cetane number of the fuel.

Such a compression combustion engine presents a number of challenges toits designer, including:

-   -   variances in cetane rating of the fuel being used must be        accounted for;    -   variances in fuel, atmospheric, and injection abnormalities must        be accounted for;    -   all cylinders should be controlled to deliver substantially        equal power;    -   resonances in the entire drivetrain, comprising engine,        transmission and propeller, need to be avoided;    -   indication of degradation in engine components need to be        provided to the pilot as a warning or a caution; and

Indicated Mean Effective Pressure (IMEP) should be calculated as anindication of engine condition during engine run-ups prior to gettingairborne.

There is a need worldwide for an aero engine that can operate on suchfuel, yet avoids the challenges noted above.

SUMMARY OF THE INVENTION

The compression combustion engine of the present invention meets theaforementioned needs. Additionally, the compression combustion engine ofthe present invention meets these needs while at the same time providingthe following features deemed necessary for such an engine tosatisfactorily operate in the aero environment.

1. Combustion chamber pressure sensing (CCPS) can be integrated intoaero Diesel engine management (the control system of the presentinvention) for the purpose of an ideally closed-loop injection system(but also open loop) that will be able to compensate for variances incetane in the worldwide Diesel/Jet fuel stream.

2. By viewing the combustion event with combustion chamber pressuresensing, the injection timing and pulse width can be adjusted real timeto compensate for variances in fuel, atmospheric, or injectionabnormalities. The injection signal can be modified to compensate andtime the peak cylinder pressure, breadth, and timing of the combustionevent.

3. Combustion chamber pressure sensing can be used to balance the poweroutput of an engine by ensuring that all cylinders are deliveringlikewise performance.

4. Combustion chamber pressure sensing can also be used to allow maximumengine performance from each cylinder without exceeding limits that maycause engine damage.

5. Combustion chamber pressure sensing can “combine” the individualcontributions from cylinders in a way that the resultant overall torquesignal does not resonate with known system natural frequencies (naturalfrequencies of the engine, transmission and propeller as a unit). This“off tuning” is relevant for harmonic disturbances that might otherwisecause resonance.

6. Combustion chamber pressure sensing can be used as a predictivemaintenance tool to determine injector degradation and warn the pilot ofan impending failure, compression testing, or weak cylinder performance.Since the current (prior art) systems approach is to provide anelectrical signal which is correlated to provide a certain quantity offuel, there is no provision for delivery discrepancies due to mechanicaldegradation of the injector and/or fuel supply.

7. Combustion chamber pressure sensing can be integrated with theinjection system in closed or open loop fashion to minimize harmfulengine dynamics that might excite propeller system resonance. They canbe used to check the harmonic content of the pressure “signal” suppliedby the cylinder.

8. Multi-pulse strategies can be used in combination with CCPS data todetermine a pressure rise compatible with engine harmonics andstructural strength. Combustion chamber pressure sensing can be used toalter the torque signature when approaching a potential naturalfrequency of an engine system.

9. Using CCPS data, the control system can be used to calculateIndicated Mean Effective Pressure (IMEP) of an aircraft or helicopterengine during “run-ups” prior to take-off at the field. IMEP data is thebest indication of engine performance, and can be used as a “pilot aid”for flight planning. Combustion chamber pressure sensing can beintegrated by the control system to ensure that sufficient energy isrejected to the turbocharger to sustain low power flight and sufficientboost pressure levels.

10. Combustion chamber pressure sensing can be integrated by the controlsystem to determine when multi pulse strategies should be switched basedon the combustion signature of the engine.

11. Combustion chamber pressure sensing can be used by the controlsystem to determine bearing loads in a real time environment, andthereby avoid engine damage.

The present invention is a control system for an aero compressioncombustion drive assembly, the aero compression combustion driveassembly having an engine member, a transmission member and a propellermember, the control system including a sensor for sensing a pressureparameter in each of a plurality of compression chambers of the enginemember, the sensor for providing the sensed pressure parameter to acontrol system device, the control system device having a plurality ofcontrol programs for effecting selected engine control and the controlsystem device acting on the sensed pressure parameter to effect acontrol strategy in the engine member. The present is further a controlmethod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the aero compression combustion driveassembly of the present invention mounted on a test stand;

FIG. 2 is a graphic representation of how injection pulse strategyaffects pressure development in a compression chamber;

FIG. 3 is a graphic representation of pressure data derived from acombustion chamber pressure sensor coupled to the engine of the aerocompression combustion drive assembly of the present invention;

FIG. 4 is a schematic depiction of a degraded injector above and anormal operating injector below;

FIG. 5 is a graphic depiction of the harmonic decomposition of anindividual cylinder by Fourier analysis;

FIG. 6 is a spring mass representation of an exemplary aircraftdriveline;

FIG. 7 is a depiction of a first order bending mode of an aluminumpropeller blade;

FIG. 8 is a simplified Diesel cycle diagram;

FIG. 9 is flow diagram for engine control in a descent;

FIG. 10 is a diagram of an exemplary combined inertial and gas loadingfor a conrod bearing;

FIG. 11 is a schematic view of the engine and control system of thepresent invention;

FIG. 12 is a graphic representation of how cetane number (CN) affectpressure rise;

FIG. 13 is a graphic representation of the use of the pressure signal todetermine its centroid shift in the time domain;

FIG. 14 is a graphic representation of the cetane in fuel with threecalibrations that are possible injection strategy changes based on theCCPS feedback loop;

FIG. 15 is a depiction of the use of CCPS to check threshold limits ofmaximum pressure and rate change in pressure due to cetane to determineabnormal combustion;

FIG. 16 is a graphic representation of the cetane effect on ignitiondelay and peak cylinder pressure;

FIG. 17 is a graphic representation of the centroid method toapproximate ignition timing shift;

FIG. 18 is a flow diagram for injection strategies for low powersettings;

FIG. 19 is a diagram indicating interaction of FIGS. 19a -19 d;

FIGS. 19a-19d is a flow diagram for CCPS data integration in controlsystem software;

FIG. 20 is a diagram of the steps of the control system software ofFIGS. 19a -19 d;

FIG. 21 is a flow diagram for injection strategy modification based ondrivetrain frequencies with speed feedback for a crankshaft sensor;

FIG. 22 is a flow diagram for injection strategy modification based ondrivetrain frequencies with torque feedback from coupling torque sensor;

FIG. 23 is a graphic depiction of a linking multi-pulse injection tocylinder pressure development in an engine control strategy;

FIG. 24 is a graphic depiction of a detecting injector malfunctions withthe CCPS;

FIG. 25 is a graphic depiction of an EPS calculated IMEP (GasHorsepower) with CCPS equipment eliminating guess-work;

FIG. 26 is a graphic depiction of a performing compression test on allcylinders with CCPS during starting; and

FIG. 27 is a graphic representation of an engine combustioncharacteristics to determine if resonance is likely to be present.

DETAILED DESCRIPTION OF THE DRAWINGS

The compression combustion drive assembly of the present invention isshown generally at 100 in FIG. 1 and comprises engine member 102,transfer member 104 and propeller 106, the propeller 106 having threeblades 108, in this particular example.

The use of combustion chamber pressure sensing (CCPS) has alloweddevelopment of a control system (described in detail below) of theengine member 102 to solve many issues particular to the field ofaero-Diesel engines by integration of open/closed-loop fuel injectioncontrol. See FIG. 2. Specifically, the control system has allowed thefollowing to be addressed:

-   -   Fuel injection quantity and timing, bias of multi pulse        strategies, and timing to address a widespread variation in        available “Jet Fuel” stream worldwide.    -   Optimization of fuel quantity and timing to balance performance        on a cylinder-by-cylinder basis to deliver the optimum fuel        economy that the application demands.    -   The ability to monitor injector degradation over time as a        performance, safety and predictive maintenance feature in aero        Diesel engines.    -   A feedback mechanism to tune the cylinder pressure and hence the        torque delivery quality of the engine. The torque harmonic        content can be tuned to attenuate the particular vibration        characteristics of the propeller and/or drivetrain resonance.

Determination of switching turbocharger control strategies for variousaltitudes and missions.

-   -   Indirect control of the amount of heat rejection to the        turbocharger to maintain boost at low power settings necessary        for extended descents, and go-around landings.    -   The determination of when to switch injection strategies for        reliability and noise vibration and harshness (i.e. multi-pulse        bias and/or count).    -   Using real time Indicated Mean Effective Pressure (IMEP), or        average pressure over the cycle data to determine available        power for take-off (airplane) or hover performance at any        altitude or atmospheric condition.    -   Controlling maximum bearing loads via pressure measurements to        prevent engine damage.

“Rate Shaping” the pressure rise to avoid resonance in the enginedriveline and accessory systems.

The control strategies developed for the present invention integratecylinder pressure sensing as a feedback mechanism in the enginemanagement computer system (the control system). By evaluating theactual combustion results, and altering the injection events to meet thecombustion targets, the control system of the present invention hasachieved a superior and quantifiable combustion.

The data shown in FIG. 3 depicts actual testing performed to calibratean aero Diesel engine. The utilization of such data makes the enginesubstantially “impervious” to worldwide fuel discrepancies. FIG. 3depicts an injection event with time along the X axis and injectionvolume along the Y axis. The top trace depicts two spaced apartinjection pulses and the bottom trace depicts the pressure curve.

Balancing Engine Cylinder Performance

Any multi-cylinder engine is a collection of cylinders that share acommon crankshaft. Although the cylinders may be dimensionally similar,the shared systems may cause discrepancies in engine performance on acylinder-cylinder basis. Sources for these differences include, but arenot limited to the following items:

-   -   Airflow differences due to a shared manifold, and/or valve        timing    -   Exhaust differences due to shared manifold and/or valve timing    -   Location of the fuel injector relative to the manifold and/or        timing    -   Thermodynamic differences due to local heat differences    -   Many other geometric factors

Any of these parameters may cause performance differences unique to aparticular engine. Since the safety of many aircraft missions depends onreserve power to execute short take-offs on runways of limited distancesor obstacles, performance optimization is essential.

The ability to measure individual cylinder pressure gives the controlsystem of the present invention the ability to trim fuel requirements tobalance the contribution of individual cylinders to the overall enginesystem. In such a scenario, the individual cylinder performance can bematched (or mismatched) to provide the required performance levelrequired.

In such scenarios, the following is achieved with feedback mechanismsfrom the individual cylinder CCPS systems:

-   -   Maximum cylinder performance from each cylinder for maximum        performance    -   Smooth engine torque delivery by balanced performance    -   Limited cylinder pressure to ensure bearing life with various        firing order combinations    -   Specific “off-tuning” to avoid harmful harmonics that may damage        driveline components    -   Minimum noise from coordinated combustion between the cylinders

The previous items are just a sample of strategies that may becontemplated when CCPS input data is available.

Monitoring of Injector Performance Degradation Over Time

In diesel engines the injector is primarily responsible for theintroduction of heat energy into the cylinder system. Modern fuelinjectors are very advanced technology. They operate at pressures thatapproach 2000 bar. They are able to cycle on/off in extremely short timeperiods approaching 1-2 milliseconds. The injection fuel quantity mayvary between 1-50 mm³ per injection. The injector orifices can vary from0.060 to 0.120 mm. With this level of precision, it is evident that asmall amount of debris or erosion can degrade performance of theinjector and affect the quantity and/or character of the fuel spraypattern.

Since the quantity of the fuel injected is determined by electricalpulse duration, the fuel delivery may not remain consistent over thelife of the engine. Variation can be detected by the informationprovided by CCPS sensor technology integrated into the control system ofthe present invention.

A deviation from the anticipated combustion pressure curve couldindicate a plugged injector, and reduced performance for the engine.This would be vital information to a pilot of a light aircraft orhelicopter, and could prevent loss of life and/or damage to the aircraftor surroundings. Note the degraded injector in the top image of FIG. 4as compared to the normally operating injector in the bottom image. Asystem that detects injector performance degradation over time is a veryuseful preventative maintenance tool.

Using CCPS Technology to Affect Engine Torque Delivery for EnhancingLife of Propeller and Accessory Systems

Aircraft engine drivelines are quite different from automotivedrivelines in several ways. For example, an automotive driveline tendsto become more massive as torque is multiplied until the point where thetire comes into contact with the road surface.

In contrast, aero drivelines are designed to be as light as practical.The size of shafting, gears, and structures is increased when torque ismultiplied. However, the driveline is designed to be compliant so as notto deliver harmful torque spikes that may cause the lightweightpropeller blades to resonate. Since diesel engines operate with peakcylinder pressures as much as 3-4 times that of their gasoline aeroengine counterparts, torque harmonics are a significant concern in anyaero diesel application. See the complex branch system depicted in FIG.6 with propeller stiffness being considered.

FIG. 5 is a depiction of a Fourier de-composition of a sample enginepressure rise. The cyclic curves below, when scaled and added willapproximate the top curve exactly. The steeper the pressure rise is, themore high order content will be required to resemble the gas curve.

Highly stressed structures such as propeller blades, tend to have a highstrength-to-weight ratio which results in a high natural frequency (withlittle damping to arrest their movement). An aluminum propeller willresonate if the torque impulse is equal to its own bending naturalfrequency. Its failure is imminent if the periodic disturbance iscontinued.

High performance Diesel engines exhibit extreme pressure rises ascylinder pressure increases from manifold pressure to near 200 barduring the combustion cycle. Fortunately, extensive development effortshave resulted in fast acting injectors. Multiple injection pulses can beused to “round off” the pressure rise, and reduce its shock to thedownstream components. This results in a dramatic reduction in structureborne “combustion noise” but more importantly reduces the stress onpistons, con-rods, bearings, crankshafts, valve train and other aircraftspecific components such as reduction gears, propeller governors, andpropellers while increasing the useful work.

By examining the pressure signal of a running engine, the control systemof the present invention includes tuning strategies to avoid harmfulharmonic content that may cause significant propeller blade stress,gearbox fatigue, and accessory damage.

Depending on the pitch angle, torsional resonance can cause a propellerblade to resonate in a bending mode. See FIG. 7. The stress can bemultiplied many times without sufficient blade damping, in a phenomenoncalled resonance. In crystalline structures (as are prevalent inmetallic propellers) there is very little damping. The reader may notethat as resonance is approached, stress can be multiplied (as in thecenter of the blade in FIG. 7) and may exceed the empirical fatiguelimits of the material. From our experience, this will drasticallyreduce the life of the propeller blade and hub. In fact, major aluminumpropeller suppliers will not “pass” a propeller in validation testing iftheir stress limits are exceeded.

Electronic control of the fuel system is able, in part, to soften the“impulse torque” input to the propeller system, as is described below.

A typical aircraft engine in the last 70 years have been “placarded” toavoid operation at various speeds for extended time periods. This wasdone to simply allow the aircraft pilot to avoid resonance by “passingthrough” dangerous areas quickly. A placard available in the cockpitindicated to the pilot which engine regimes to avoid.

The present control system processes combustion data and does ananalysis to determine harmonic content of the gas curve. If a criticalspeed for the propeller system is approached, the control system actingon the injection system “deadens” the combustion by exercisingappropriate control of the engine injectors to minimize the harmoniccontent of the torque impulse, and prevent propeller and/or systemsdamage resulting from resonance.

Determining Turbocharging Control Strategies for Various Altitudes andMissions

Turbocharger control has become a large part of engine tuning where highperformance is required. Turbocharger maps look a lot like topographicmaps with “efficiency islands” indicated.

The highest practical limit for a single stage turbocharger is in thevicinity of 4 bar pressure ratio. Fortunately, turbochargers naturallycompensate for a rarified atmosphere by speeding up with an increase inelevation. This feature sounds practical until the “speed limit” isreached at high elevations. The upper limit is a speed that beyond whichthe turbocharger wheel may burst due to high centrifugal loads.

In order to operate an aero Diesel at high elevation (25,000 ft. MSL) adual stage turbocharger is likely required. Typical automotive Dieselengines already have explored staged turbo charging as a means ofreducing engine size and fuel consumption for cruising at highwayspeeds. In an aircraft application a similar scheme is adopted to reduceengine size for weight reasons. In this case, it is necessary to monitorthe switching of the secondary turbocharger to keep each systemoperating near its optimum efficiency island.

The use of sequential turbo charging is necessary to operate at highaltitudes. One feedback input to the control system is the actualturbine speed. But utilizing the CCPS data, the control system enableslooking at the character of the combustion curve to determine when to“activate” the secondary turbocharger. Since “injection delay” is anindication of the air motion in the combustion chamber, a slow delaywould indicate lack of mixture motion. This threshold is then used totrigger the secondary turbocharger bias.

Use of Real Time Indicated Pressure to Calculate Available Power forMission Critical Flights

One aspect of a pilot's responsibility is to calculate the weight andbalance of his aircraft for flight planning purposes. With the use ofCCPS instrumentation, the actual performance of the engine can becalculated by the control system before takeoff, during a normal engine“run-up”.

The pressure trace from the individual cylinders can be used tocalculate the power available based on indicated mean effectivepressure. The indicated mean effective pressure is an average pressureover 720 degrees in a 4-cycle engine. IMEP is the best indication of theavailable power from an engine. It does not take friction into account,but is a very good estimation for the power available on the takeoff runor hover calculation for light helicopters. An alternative approachwould approximate power accurately using and indirect approach. Analternative scheme would use peak cylinder pressure, pressure rise, andtiming of the peak cylinder pressure to determine the available powerindirectly.

The control system integrates CCPS data into its management system as apilot aide to determine available power at takeoff.

Piston helicopters also benefit from such data. One of the criticalaspects to the helicopter pilot is the ability of the helicopter tohover out-of-ground-effect. The hover capability of a helicopter isprimarily determined by gross weight, engine power, and elevation(density of air). It can be dangerous to lift off in ground effect, andthen transition to flight without ground effect (off a cliff orbuilding). If there is insufficient power to sustain lift, thehelicopter will descend, and may crash to the ground before the pilotcan take control of the situation. A CCPS would be the most accurate wayto determine engine performance before leaving the ground, and thus ahuge safety feature.

One of the problems that have been associated with Diesel engines issustaining a healthy combustion during long descents at low powersettings. Some notable Unmanned Aerial Vehicles (UAVs) have encountered“frozen combustion” during long low power descents. UAV's areparticularly prone to these phenomena due to their design as a“loitering vehicle”. They are essentially gliders with engines to assistin the mission. The engines are used to sustain flight and generateelectricity for the electronic surveillance and flight controls.

The simplified Diesel cycle diagram in FIG. 8 depicts the heat leavingin the exhaust as indicated in the term Q₂. The quantity of heat in theexhaust is determined by the residual amount of fuel from the lastinjection pulse, and the timing of the exhaust valve opening asindicated by “d” in the diagram.

In conditions where the actual power produced from point “c” to “d” isminimal, the CCPS data is a very useful tool to determine if thecombustion is “healthy” or in danger of “flaming out”. Utilizing theCCPS data, the control system may choose to add additional fuel near theend of the expansion, not to produce power, but to sustain sufficientmanifold pressure for the engine to have on reserve. Since the engine isnot producing crank power in this mode. The intent of a “post Injectionpulse,” is to keep the turbocharger speed up regardless of the engineoutput required. Having immediate boost is desirable for “missedapproaches” when a pilot needs to add power immediately for a “goaround”.

The control system utilizing CCPS technology is used to maintain“healthy combustion” during low power descents. With a combination ofturbo speed, cylinder pressure, and ambient pressure, the software canmaintain these healthy conditions. The ambient pressure sensor cantrigger the software if the aircraft is in a descent mode, based on thepressure altitude. Low power settings can be determined with IMEP valuesin conjunction with the turbocharger speed. In the case when bothconditions are low.

To maintain a healthy manifold pressure and keep the turbochargerspooled up, added energy in the form of fuel is necessary. An added fuelinjection towards the end of the combustion cycle will create therequired energy to spool up the turbocharger and create a highermanifold pressure. See FIG. 9. This will be checked by the software andcorrected if needed by changing the timing and trimming of the pulsewidth. The software runs this in a closed loop until the healthycombustion is achieved or flight plan changes (e.g. high power settingis demanded). FIG. 9 shows the flowchart of the control software toeffect the above.

Using Combustion Chamber Pressure Sensing to Determine When to SwitchInjection Pulse Strategies

The control system of the present invention alters the pulse strategyand dwell of each event in an effort to maximize the delivered torque,and alter its character based on readings from integrated CCPS elementsin the cylinder head.

For example, the control system may choose to add an “after injection”pulse of fuel. This pulse is used to sustain turbo speed in highaltitude operations. Any combination of pre-injection pulses and maininjection pulses may be used to rate shape the cylinder pressure rise tosoften or avoid troublesome harmonics, and increase useful work andefficiency.

Using Combustion Chamber Pressure Sensing to Limit Bearing Loads andPrevent Engine Damage

In any engine, the loading of its bearings is directly related to thecylinder pressure and the area of the piston. The product of thepressure (P) multiplied by the area (A) of the piston gives theinstantaneous gas force of the piston. Actual bearing loading depends onthe inertial properties of each component as well.

The control system can draw conclusions about bearing loading based onCCPS cylinder pressure data as acted on by the control system as a meansto limit the gas force applied in certain modes of engine operation.

One example is to a main bearing that is loaded “twice” by adjacentcylinders in a multi-cylinder configuration. In this example, the oilfilm may be diminished considerably when adjacent firings are from thesame bank of cylinders.

Cylinder pressure varies with engine output. Since the gas force isproportional to the injected fuel, and combustion characteristics, it isuseful to know what its magnitude might be. The control system, usingintegrated CCPS data, can give insight to the combustion magnitude, andthe subsequent bearing loads. Since the component inertial loading andthe speed is known, an exact bearing load can be determined with gasforce data. This can prevent premature bearing failure by warning theoperator of bearing overload.

FIG. 10 is a depiction of how a lower connecting rod bearing is loadedwith inertial forces (egg shape) and combined with a gas force (topportion) component. The inertial forces are easily calculated withcomponent mass, speed, and geometry, while the gas forces depend on theproduct of actual combustion pressure and piston area. Combustionchamber pressure sensing allows insight into the loading of the internalengine components.

A diesel engine member 102, as depicted in FIG. 11, includes a pluralityof cylinders 120. In a preferred embodiment, the engine 102 is a flatconfiguration, having four cylinders in a first bank and an opposed bankof four additional cylinders. The engine 102 of FIG. 1 is of suchconfiguration. Each of the respective cylinders 102 has a combustionchamber 122. A fuel injector 126 is disposed in each of the respectivecombustion chambers 122. Fuel is supplied to each of the respective fuelinjectors 126 by a common rail 128.

The common rail 128 is fluidly coupled to a high pressure pump 130. Thehigh pressure pump 130 is fluidly coupled to a fuel tank 132. A fuelfilter 133 may be interposed between the fuel tank 132 and the highpressure pump 130.

An electronic injector control 134 is coupled to each of the respectivefuel injectors 126, each of the respective fuel injectors 126 beingsusceptible to electronic control for timing and pulse width control.The injector control 134 is operably coupled to a control system 136.

A CCPS sensor 138 is operably coupled to each of the respectivecombustion chambers 122. Each respective CCPS sensor 138 is in turnoperably, electronically coupled to the control system 136. Data sensedby each respective CCPS sensor 138 is thereby provided to the controlsystem 136. It is understood that the control system effects control ofthe injectors individually responsive to the data received from the CCPSsensor 138 that is mated to the combustion chamber 122 that is served bythe respective fuel injector 126.

The engine member 102 additionally has at least one turbo 142 fordelivering a charged air supply to the respective combustion chambers122. A turbo control 144 is operably coupled to the turbo 142 and to thecontrol system 136. By this means, the control system, using datareceived from the CCPS sensors 138. Communicates commands to the turbocontrol 144 for control of the turbo 142 as desired.

The engine 102 of the present invention preferably utilizes a PressureSensing Glowplug as CCPS 138 in each cylinder for the purposes ofmonitoring cylinder pressure in the engine. The CCPS sensor 138 is usedas an analog input to the control system 136.

The use of CCPS technology as a feedback in real-world installations canoptimize engine calibrations for a variety of conditions.

The focus of CCPS integration into the control system in thisapplication is to identify the strategies of utilizing this technologyfor the benefit of aviation Diesel applications. The work in thisapplication therefore focuses on the “WHEN” and “HOW” pressure isdeveloped in a Diesel aircraft engine. The information obtained fromCCPS input is used to optimize efficiency, provide for reliability,improve pilot information, and diagnose injection systems for predictivemaintenance. These aspects all have the focus of improving GA andUnmanned Aerial Vehicle (UAV) safety by using electronics to the pilot'sbenefit.

How Fuel Quality Affects Pressure Development in Diesel Engines

Cetane is a quality in kerosene derivative fuels that defines howrapidly combustion occurs in a Diesel engine. A high cetane number meansthat the fuel will begin to ignite rapidly and continue burning in acontrolled fashion. Low cetane fuel will ignite more slowly, and thencause a rapid pressure rise as the piston approaches Top Dead Center(TDC) in an engine.

The CCPS sensor is particularly useful in identifying some of thecharacteristics of combustion with low cetane fuel. There are threecharacteristics that are noticeable immediately. The reader may note byexamination of FIG. 15 that low cetane fuel has a longer ignition lag,but once ignition starts, the energy in the fuel rapidly combusts.

The CCPS sensor in combination with a crank speed sensor can determineif the combustion process is within set limits for “normal” combustion.An increase in the slope of the pressure curve (dP/dt) may indicate oneor more of the following:

-   -   The aircraft was fueled with a low quality Jet fuel    -   Large quantities of bio-fuel (largely uncontrolled) are present        in the fuel supply    -   Perhaps gasoline was mistakenly pumped into the aircraft fuel        tanks    -   Other elements of the fuel injection system are in need of        maintenance

There are other significant characteristics that may be determined withCCPS sensors 138. Examination of FIG. 12 shows that typically theincreased ignition delay or lag results in a change of the peak cylinderpressure timing point, which may be referenced to TDC or some otherfixed point.

Since the injected fuel quantity is closely calibrated with themechanical injection system, and the heating content of varying Jetfuels are not different, when the fuel does combust, it tends to reach ahigher peak cylinder pressure. Thus low cetane fuel combustion (See FIG.12) can be “sensed” in one of three ways:

1. Higher than “normal” pressure rise per crank angle (dP/dt)

2. Longer than “normal” time for peak cylinder pressure to occur (longignition delay or lag)

3. Higher than “normal” peak cylinder pressure

The boundaries of what is “normal” is selected and implemented in thecontrol system 136. The CCPS 138 can be used in conjunction with a cranksensor to measure pressure against a time function for combustionevaluation. In particular, the period of combustion pressure developmentcan be integrated by the control system 136, with the intent ofevaluating the point where the combustion is effectively “centered” inits development time period. This can be done to effectively perform anintegration of the pressure function during its development. Thispressure development shape is depicted for each type of combustion inFIG. 13.

Using an integrated shape as noted in the lower right corner of FIG. 13is a useful way to determine an actual phase shift in injection timingthat can place the peak cylinder pressure back in its usual location.This method of estimating angular timing shift is more accurate thantrying to locate the angular point of highest pressure in each case.

Another method is to accurately determine the “peak pressure” in thevicinity of the anticipated peak cylinder pressure by looking for thepoint when dP/dt is effectively “zero” and using that point and the meanslope for a period preceding the peak cylinder pressure in time. In thisfashion we can also obtain using timing information for peak cylinderpressure location, and the development character of the cylinderpressure, or dP/dt.

Adapation of Injection Strategy to Compensate for Low Quality (LowCetane) Fuel

The control system 136 injection strategy relies on the CCPS 138 todetect particular threshold conditions associated with abnormalcombustion due to poor quality fuel. The particular threshold limitsare:

-   -   An abnormally high/low change in pressure per crank angle        (dP/dt) for a given engine speed and load (propeller governor        setting) map    -   An abnormally high/low peak cylinder pressure (P_(max)) for a        given engine speed and load (propeller governor setting) map

When either (typically both) conditions above are sensed to be out oflimit by the CCPS element, our strategy indicates that we are runningwith a lower/higher quality fuel than anticipated. A control strategy isimplemented at this instant in time.

The general approach of the control strategy is to adjust the “timing”and the “trim-quantity per pulse” of the fuel to bring back the pressurecurve within the threshold limits of what is considered to be “normal”or “preferred”. The present engine 102 will operate with the bestefficiency, run quality, noise level, reliability, and less wear when itruns within the prescribed limits as determine by a selectedcalibration. A normal condition may be as depicted as case (3), defaultcalibration, in FIG. 14.

When abnormal combustion (case 1) is detected by the control system 136using CCPS 138 data, the immediate response of the control system 136 isto alleviate the P_(max) and dP/dt condition which may cause structuraldamage to the engine by resonance, or bearing overload in particular.The low cetane conditional effects are of more concern than that of thehigh cetane condition. By close examination of FIG. 15, the reader maynote the dramatic effects of ignition lag, which leads to excessivepressure development (dP/dt) and excessive peak pressure P_(max). Thereader should note at the bottom of FIG. 15 that needle lift (and hencefuel quantity) is exactly the same, regardless of fuel quality. Theabove portions of this diagram indicate how heat release andconsequently cylinder pressure development are affected. Thresholdlimits are developed by surveying fuels of varying Cetane Number (CN),to determine the threshold limits for combustion schemes.

A timing correction initiated by the control system 136 to the injectionscheme may be required initially to compensate for the greater ignitiondelay of low quality fuel. Similarly, an adjustment may be made for highcetane fuel, depending on the limits set for the combustion pressureP_(max) and slope dP/dt. In either case, an adjustment may becontemplated by determining the angular position limits of the Peakcylinder pressure (as in FIG. 16) or by a more sophisticated method todetermine the “centroid” of combustion (as shown in FIG. 17).

With a medium quality fuel, a timing adjustment may be all that isrequired to keep the combustion within the limits specified within thecontrol system. With low cetane fuel the quantity of the injection pulsemay need to be trimmed to bias a higher fuel delivery earlier in time.This is termed “trimming” the fuel map. This condition is depicted ascase (2 timing and/or trimmed) at the bottom of FIG. 14. In each case,the effect of timing or trimming strategy is “checked” by the controlsystem 136 in real time for either/both P_(max) and dP/dt.

It is recognized that the presence of certain low cetane (bio fuels) inthe Jet fuel supply may make it impossible to maintain the requiredpower within the cylinder pressure limits specified. In this particularcase, a multi-pulse strategy change may be required as depicted in case(3), to bring the combustion back to what is considered “normal” forhigh cetane fuel in FIG. 14. A change in strategy may involve using oneor a combination of pulse strategies as specified in the lower portionof FIG. 14 or the lower right portion of FIG. 23. The decision as towhat pulse strategy will accomplish the task will be determined intesting and calibration activities.

The strategy of the present invention for the integration of CCPSsensors 138 into the control system 136 as an injection modificationstrategy is contained in the flow chart of FIG. 19 and FIGS. 19a-19d .The functional description of the process is contained in FIG. 20,(S100) Detect cylinder pressure with PSG. The pressure rise per crankangle (ΔP/Δt) is used to compare against the base map. A way to do this,is to integrate the shape into a triangular shape. The centroid of thisshape will be calculated afterwards. The peak cylinder pressure will beused to compare as well.

(S101) The actual centroid will be compared to the preferred/normalcentroid. The actual peak cylinder pressure will be compared to thenormal peak cylinder pressure. If there is a deviation or a phase shaft,a correction is needed.

(S102) If the peak cylinder pressure as well as this pressure rise percrank angle is bigger than normal, a correction is needed to advance theinjection and change pulse width.

(S103) Injection timing as well as pulse width will be changed toadvance and compensate for the deviation.

(S104) The actual centroid will be compared to the preferred/normalcentroid. The actual peak cylinder pressure will be compared to thenormal peak cylinder pressure. If there is a deviation or a phase shift,a correction is needed.

(S105) IF the peak cylinder pressure as well as this pressure rise percrank angle is bigger than normal, a correction is needed to advance theinjection and change pulse width. If the peak cylinder pressure as wellas this pressure rise per crank angle is smaller than normal, advance tostep 205.

(S106) Injection strategy will be changed, by adding an additionalpulse, to fine trim the timing as well as pulse width to advance andcompensate for the deviation.

(S107) The actual centroid will be compared to the preferred/normalcentroid. The actual peak cylinder pressure will be compared to thenormal peak cylinder pressure. If there is a deviation or a phase shift,a correction is needed.

(S108) If the peak cylinder pressure as well as this pressure rise percrank angle is bigger than normal, a correction is needed to advance theinjection and change pulse width. If the peak cylinder pressure as wellas this pressure rise per crank angle is smaller than normal, advance tostep 208.

(S109) Injection timing as well as pulse width will be changed toadvance and compensate for the deviation.

(S202) If the peak cylinder pressure as well as this pressure rise percrank angle is smaller than normal, a correction is needed to delay theinjection and change pulse width.

(S203) Injection timing as well as pulse width will be changed to delayand compensate for the deviation.

(S204) The actual centroid will be compared to the preferred/normalcentroid. The actual peak cylinder pressure will be compared to thenormal peak cylinder pressure. If there is a deviation or a phase shaft,a correction is needed.

(S205) If the peak cylinder pressure as well as this pressure rise percrank angle is smaller than normal. A correction is needed to delay theinjection and change pulse width. If the peak cylinder pressure as wellas this pressure rise per crank angle is bigger than normal, advance tostep 105.

(S206) Injection strategy will be changed, by adding an additional pulseto fine trim the timing as well as pulse width to delay and compensatefor the deviation.

(S207) The actual centroid will be compared to the preferred/normalcentroid. The actual peak cylinder pressure will be compared to thenormal peak cylinder pressure. If there is a deviation or a phase shift,a correction is needed.

(S208) If the peak cylinder pressure as well as this pressure rise percrank angle is smaller than normal. A correction is needed to delay theinjection and change pulse width. If the peak cylinder pressure as wellas this pressure rise per crank angle is bigger than normal, advance tostep 108.

(S209) Injection timing as well as pulse width will be changed to delayand compensate for the deviation. The following paragraphs amplify thefunctional description.

With the CCPS 138 measuring the cylinder pressure, the control system136 can determine dP/dt. A novel methodology for this is proposed usinga centroid to measure timing phase shift. This centroid point inrelation to the crank angle as well as P_(max) is being used in thesoftware to compensate for the different qualities of fuel. The phaseshift is determined with the centroid methodology and compared it to abase map.

Once the software of the control system 136 determines if the enginecombustion is abnormal (i.e. high or low cetane fuel quality), thecontrol system 136 software corrects for this with timing and/or fuelquantity trimming of the base injection map. If the P_(max) as well asdP/dt is higher than the corresponding parameters of the base map,retarding of the fuel injection and trimming of the pulse width isnecessary. If the values show a lower reading, a delay will be needed.In either case, one of these strategies will change the P_(max) anddP/dt to acceptable level within selected threshold limits. To get tothe desired values, timing and trimming of the fuel injection quantitywill be done and evaluated in the next step.

If the threshold value is not attained, the software will determine,once again, if the values are still too high or if perhaps thecorrection overshot the desired value. In these cases the software willopt to change the injection strategy and add an additional pulse to thefuel injection scheme. This is done to fine tune the corrections andlimit overshooting. The software will perform a correction (includingthe added pulse) in timing and trimming of the pulse.

The software will check if the corrections are done within the thresholdvalues and will determine if the values are too high or too low.According to this calculation, changes in timing and trimming of thepulse width will be done. This process will continue of in a loop untilthe fine tuning reached the desired values. In this case the engine canrun on its base map and potential damage is avoided. FIG. 19 shows adetailed flowchart of the control software of the control system 136.

Understanding the Aircraft Driveline

One of the keys to understanding a driveline is to understand the“natural frequency” of the system. Most engine drivelines have verylittle effective damping, unless a particular “damper” is designed inthe system. Most crankshafts, gears, propeller shafts are made of steelwhich is crystalline in nature. Steel has a very low internal damping,and is therefore susceptible to resonance.

Resonance is a phenomenon that is characterized by a systems' inabilityto damp periodic energy inputs that may result in a harmonic excitationof the system. Left unchecked, the system may oscillate until imminentfailure is likely.

Any driveline system will have natural frequencies that arecharacterized by the stiffness/weight of the system. The resonantfrequency of the system must be determined in order to determine whichharmonics to avoid in the operating range of the engine. Once thecritical frequencies are known, the engine speeds that might besusceptible to resonance can be predicted.

Using Software to Create Torsional Vibration Models

The first step to take in performing a dynamic analysis is to accuratelymodel the dynamic system is simplified by using packages that work withthe CAD systems to create a one dimensional torsional model. Thepropeller cannot be ignored as a part of the torsional evaluation. Ifnecessary, the one dimensional model must be modified to represent theflexible blade of the propeller.

With system mass and spring stiffness known, software or the Holzertabular method may be used to determine the resonant frequency andvibrational mode shape. The calculated frequencies and mode shapes areuseful in determining at which speeds an engine may be susceptible toresonance.

In the past, resonant conditions were “placarded” as danger zones tostay away from in normal aircraft operation. The pilot had to payspecial attention to avoid operation in these areas to avoid enginedamage.

Altering the Harmonic Content of the Gas Torque

In the case of the Diesel aircraft engine 102, there exists ability touse the CCPS 138 data and the common rail electronic injector 126 to“rate shape” the pressure curve to ensure that resonance phenomena isminimized as the engine speed changes to meet flight regimes.

At various speeds, different harmonic forcing function orders must bepresent to cause resonance. The actual amplitude of the resonance is afunction of how much damping is present in the engine system. There maybe a natural frequency (ω₀₁) to be avoided. (See FIG. 27).

At resonant speeds, the A-E pulse weighting could be altered to minimizethe harmonic content of the gas tangential force produced. This wouldcreate a gas harmonic that would be more “soft” to the natural frequencyat that particular critical speed. How to attain that level of controlis what the control system 136 utilizing CCPS 138 data permits.

The goal is to come up with a calibration that is optimized from anefficiency perspective. To that end, a modern electronic injectionsystem allows selection of a “recipe” that gives the desired “shape” toa pressure curve. Fourier analysis is used to determine what the gasforce curve is made of. Once decomposed, the gas force is determined tobe “comprised” of various elements that when added will create the exactshape of the gas torque curve.

FIGS. 21 and 22 show two strategies to control the composition of thegas torque harmonics by implementation of various fueling strategies. Ata given speed different orders may cause resonance at a variety ofengine speeds. At the low speed regime, a certain excitation force mightcause resonance, whereas in the high speed regime, a different order maybe more likely to cause resonance. With the capabilities of multi-pulsefueling schemes such as those proposed in FIG. 23, there are no“typical” amplitudes of gas torque harmonics.

In the past it has been possible to list what is “typical” in terms ofgas torque harmonic content. There is however, nothing “typical” for aDiesel engine with all of the possible fueling combinations offered bythe modern multi-pulse system of the present invention. Today, injectorsare capable of a 5-pulse strategy, but it is hard to predict what levelof control is contemplated for the future. Even with a 5-pulse strategy,there are virtually infinite ways to deliver the fuel to the cylindersystem, and the result is a gas torque curve which can be manipulated bythe control system 136 to “shape” the pressure curve development in afashion that does not promote drive line (propeller, crankshaft,accessory) vibrations.

The control system 136 of the present invention utilizing CCPS 138technology is a vital piece of equipment to be able to check thepressure development within each cylinder system. With a multi-cylinderengine, it is even possible to tune different cylinders to provide avarying contribution to the overall torque signature. With a strategylike this, the harmonic characteristic can be tuned for severalobjectives.

Using the Control System as a Maintenance Tool and Performance Indicator

The control system 136 of the present invention utilizing CCPS 138technology is particularly useful as a periodic maintenance tool for theaircraft application, where reliability is of foremost concern for thesafety of the pilot and crew. Since aircraft engines spend adisproportionate amount of time sitting, they may be susceptible to sometypes of failure modes not seen in automotive applications.

One use of the control system is to monitor the relative conditions ofall cylinders in an engine. FIG. 24 shows an actual test conditionexperienced during calibration activities of the engine 102. In thisparticular test, all eight cylinders 120 were sent the same electronicsignal by the control system 136 which should have (in theory) deliveredthe same amount of fuel to each cylinder. The actual cause of the twounderperforming cylinders was sonic phenomena (water hammer) in the fuelrail 128 caused two of the eight injectors to indicate a differentcombustion (lower peak pressure) than the other cylinders. Without thecontrol system 136, it would not have been known to pursue and solvethis piping problem in the fuel rail 128. In real world conditions, thecontrol system 136 informs the pilot that a cylinder 120 or cylinders120 was/were misfiring, and would warrant attention. The same strategywould help in determining a damaged or plugged injector as shown in thetop portion of FIG. 24, depicting the magnified tip of an injector 126.The control system 136 can be used to “balance the contribution” of allcylinders 120 when running. In another scenario, the control system 136can be tuned to provide maximum output at a maximum cylinder pressure.

In extreme cases, an underperforming cylinder 120 could set the dynamicsystem into resonance, and may damage the engine if left unchecked. Thepilot's only indication in systems without the control system of thepresent invention would be an undefined “rough running” condition thatthe pilot may/may not sense, depending on the mechanical experience ofthe pilot.

Even if the aforementioned “rough running condition” was not damagingfrom a dynamic perspective, the pilot may be down in power. While thismay not be significant in lightly loaded, low altitude take-offconditions, the condition may be lethal in high altitude, warm ambienttemperature take-off conditions.

The control system 136 of the engine has the ability to communicate realtime performance data to the pilot for any meteorological or altitudecondition he finds himself in. By computing the mean pressure over thecycle for each cylinder, and adding the contributions up, the pilot hasin-effect a built-in dynamometer in the control system 136 that willindicate maximum performance at run-up for every planned take-off. Thisinformation is a groundbreaking performance tool for flight planningmade possible by the control system 136 of the present invention.

The engine 102 of the present invention has a direct reading of engineperformance based on an Indicated Mean Effective Pressure (IMEP) valueas determined by the control system using data from the CCPS sensor.This value over time will indicate the actual expansion work done by thecombustion gas, and hence an accurate measure of available engine powerfor the weather conditions of the day. This term is defined as in FIG.25.

The aforementioned combustion measurement is not the only usefulapplication of the control system 136. With the control system 136, thepilot has the ability to check the compression of every cylinder forevery start of the engine. For example, a stuck valve would show upimmediately as a condition that would “warrant further inspection beforetakeoff”. This is possible due to the ability to scan cranking pressureswhile starting. See FIG. 26.

A number of other possible Items can be determined as well by thecontrol system 136, including (but not limited to):

-   -   Stuck intake/exhaust valves    -   Deteriorated valve seat    -   Broken or worn piston rings    -   Bad or leaking cylinder gasket    -   Leaking injector (hydro-lock impending)    -   Scuffed cylinder wall

In any or all of these cases, the control system 136 is a usefuldiagnostic and/or safety advantage for the pilot. Knowing the “health”of each cylinder in the engine system is a novel approach tounderstanding engine reliability and flight worthiness.

Using the Control System 136 to Control Turbocharger Switching

CCPS 138 technology is used by the control system 136 to control theswitching of turbochargers 142. The control system can use the actualcombustion data to determine the character of the combustion curve andwhen to “activate” a secondary turbocharger 142. Since “injection delay”is an indication of the air swirl in the combustion chamber, a slowdelay would indicate lack of mixture motion. This threshold can be usedto trigger the secondary turbocharger switching of a waste gate.

Further, the control system 136 uses CCPS 138 data to calculate thepressure rise per crank angle (dP/dt) and compare its value against thebase map. A slow delay would indicate a slower pressure rise per crankangle. The lack of mixture can be detected with a lower maximum cylinderpeak pressure. This is caused by an incomplete combustion of fuel. Thesetwo parameters assist in pinpointing the operating conditions. In thecase where more air is desired, and the secondary (high pressure)turbocharger 142 a (of FIG. 11) will be triggered. The secondaryturbocharger 142 a will charge the combustion chambers 122 withadditional air to create a better mixture swirl. By measuring the boostpressure, the control system 136 can determine when to switch off or howto trim the second turbocharger 142 a, to keep each system operatingnear its optimum efficiency island. FIG. 18 shows a flowchart of thestrategy embedded in the control system 136.

1-7. (canceled)
 8. An aircraft engine configured to tune combustionchamber fuel injection for the purpose of avoiding harmful naturalresonance frequencies of an associated drivetrain, the aircraft enginecomprising: a plurality of cylinders, each cylinder having a respectivecombustion chamber; a plurality of combustion chamber pressure sensingelements, each combustion chamber pressure sensing element associatedwith a respective combustion chamber and configured to sense arespective pressure within the combustion chamber during operation; aplurality of fuel injectors, each fuel injector associated with arespective combustion chamber and configured to inject fuel into thecombustion chamber; and a control system in communication with theplurality of combustion chamber sensing elements and the plurality offuel injectors, the control system configured to monitor combustionharmonics at least partly through the sensed combustion chamberpressures, and alter the fuel injected by the plurality of fuelinjectors to tune combustion for the purpose of avoiding harmful naturalresonance frequencies of the associated drivetrain.